Speaker Cable - A Halloween Edition of Crazy Good Advice

Hope everyone had a great Halloween! I also hope everyone is successfully recovering from the candy corn flavored, beer induced hangover that greeted them this morning. Any costume wearers? I dressed as a sound guy last night.

Appropriately enough my Halloween show marks a first in audio engineering. Never have I been terrified for my life at a venue before now. I can only hope this will be the only time this happens (this won't be the only time this happens).

I was running sound at a small venue for a local band's inaugural show. We were the opening act so we were setting up in a more or less empty venue with ample time to spare, which was actually quite nice, but that was about where the pleasant surprises ended.

Like all small venues everything technical is backwards and half broken but I came in expecting that. What I wasn't expecting was the nasty surprise lurking in the corner while I was trying to diagnose a faulty wedge. In the dark corner of the stage, shadowed by the precariously stacked PA speakers was the blood-chillingly terrifying connections for the speakers... instrument cables.

SNAAAAAKE!!

To really understand what's so frightening here, you must know something about passive speakers. Unlike what is most likely hooked into your computer right now passive speakers do not have any active circuitry inside the speaker enclosure. The actual voltage that drives the speaker comes from a separate amplifier that transmits the full speaker level signal through wires to the speaker cones to make sound. In the case of this PA, there were 4 channels running at a total maximum peak of 1000W of signal, so assuming power was evenly divided between each channel (it wasn't,) each of those four instrument cables were running about 250W or more at certain parts of the show.

The wattage isn't a problem in and of itself, the problem was that these were all coaxial audio cables, meaning the signal wire is surrounded by a cage of grounded wire to help shield the signal from outside interference. This is more commonly called instrument cable, the same thing that is plugged into a guitar. 

An instrument cable. That little tiny copper line carries all the signal. The ground shield just hangs out.

These cables are made for low level voltage, not a kW level PA. 250W doesn't sound particularly scary unless you look inside a guitar cable and realize all that power is running through a wire bundle about as wide as your thumbnail is thick.

Literally every single manual that comes with passive speakers, including guitar cabinets and PA amplifiers, expressly state that instrument cables cannot be used for this type of a connection. Speaker cables use conductors quadruple this size, offering 12 times the conductive surface, in order to safely carry speaker level power.

Speaker cable holds a pair of the same type of wires you'd expect to find in your house. At speaker level wattage shielding isn't as important.

After confirming I was indeed dealing with a severely miswired PA system I brought the band together, taking time out of our load in and sound check, to explain that there were very real dangers involved with playing this show. The band got on stage, I ran the mix as quietly as I could possibly get away with, we watched a few following acts that gave us high praises then high-tailed it out of there before the house engineer clipped his way into an electrical fire.

I try to be mildly funny with these posts but I must make this abundantly clear, I was scared for my safety and the safety of everyone in there. I've now included a fire extinguisher on my list of things to take to an unfamiliar venue and will likely offer alternate locations to my clients. Good luck getting me back over there.